math

The rails on a railroad are 30 feet long. As the train passes over the point where the rails are joined, there is an audible click. The speed of the train in miles per hour is approximately the number of clicks heard in:
A. 20 seconds
B. 2 minutes
C. 1.5 minutes
D. 5 minutes
E. None of these

How to get a relation between the number of clicks and speed of the train and the time taken by it.

I assumed that the number of clicks has to be an integral value like 1,2,3..... Further i tried to figure out at what distance and at what time the train gives an integral value of the number of clicks. I tried to play with the options.But all in vain.

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asked by Gaurav
  1. Please help....

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    posted by Gaurav
  2. See how many clicks in 1 minute at 60 mph

    60*5280/30*60=176 clicks in 1 minute

    But they want to know how many seconds for 60 clicks to occur:

    60/176=About 1/3 of a minute, 20 seconds

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    posted by KentG
  3. 30 ft (1 m/5280 ft) = .00568 mile

    v = .00568 /T in hours

    T in hours = .00568 /v

    T in seconds = 3600*.00568/v
    = 20.45/v

    clicks/second = 1/T = v/20.45
    so
    v = 20.45 * clicks/second

    1 click/second --> 20.45 mph
    2 clicks/second -->41 mph

    v = 20.45 * clicks/second
    = clicks/20.45 seconds

    so A.

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    posted by Damon

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